1. Field of the invention
The present invention relates to a switch, an image transmission apparatus, an image transmission method, an image display method, an image transmitting program, and an image displaying program.
2. Description of the Related Art
As the processing capacities of computers have dramatically increased, computers are being more and more widely used. It is not unusual today for an individual user to own more than one computer and use each computer in a different work environment. In such a case, the input/output devices such as a keyboard, a display, and a mouse, are connected to the computers through a switch, so as to save space and reduce costs.
The switch is generally called a KVM (Keyboard, Video, and Mouse) switch. The switch is provided between the input/output devices and the computers, and connects the input/output devices to only one of the computers. A user can operate the switch to select one of the computers to be connected to the input/output devices.
With the above conventional switch, however, it is necessary for a user to operate the mouse and keyboard connected to the switch, and therefore, the user has to stand by the mouse and keyboard at all times. So as to eliminate such an inconvenience, a switch that can be remotely operated has been developed.
With a remotely operated switch, it is possible for a user to access a computer connected to the switch not only from the mouse and keyboard connected to the switch, but also from a personal computer that is located in a remote place over a network. Japanese Unexamined Patent Publication No. 2001-344189 (hereinafter referred to as Patent Document 1) discloses an example of the conventional remotely operated switch. With the switch disclosed in Patent Document 1, a user can remotely switch computers from another computer equipped with an input device.
Japanese Unexamined Patent Publication No. 9-69010 (hereinafter referred to as Patent Document 2) discloses an image display technique relating to a switch. In a central monitor controlling system disclosed in Patent Document 2, a personal computer connected to the host computer over a network is used as a remote terminal, and image display information is transmitted to the display of a computer through an X-Window system. The remote terminal is operated with a mouse, and the host computer is notified of each screen switching operation through a keyboard. In this manner, the display of the computer can have the same screen display and functions as the monitor controlling display of the host computer.
Japanese Unexamined Patent Publication No. 3-48922 (hereinafter referred to as Patent Document 3) discloses a cursor controlling technique, though it does not relate to a switch. A pointing cursor predictive moving device disclosed in Patent Document 3 detects the history of movements of the mouse cursor, and predicts the final destination. The pointing cursor predictive moving device then moves the cursor directly to the icon located at the final destination, thereby shortening the cursor moving time.
With any conventional switch, however, the analog image output of each scanning line is converted into digital signals which are then transmitted to a remote-control computer connected to the network. Therefore, as the image to be transmitted widens, the time required for the A/D conversion increases, resulting in a decrease of the frame rate. The frame rate varies with the conversion processing speed. When the frame rate decreases, a pointing-type display involving a mouse cursor has a poorer pointing accuracy.
In some conventional switch, image data that are inputted from a selected computer are acquired at 1/n of the scanning frequency F (1≦n<F), and the acquired image is compared with the previously acquired image. As a result of the comparison, a line or a block including the different part is extracted, and the extracted line or block is transmitted to a remote-control computer. By this method, the entire image is checked for a difference, and therefore, the frame rate decreases as the image size increases. Also, when there is a great change in the image, the frame rate decreases. As the frame rate decreases, the mouse cursor display updating frequency drops, resulting in a poorer pointing accuracy.
With the pointing cursor predictive moving device disclosed in Patent Document 3, the cursor moving time can be shortened, but a decrease of the pointing accuracy due to a frame rate decrease cannot be prevented.